Re: Configuring synchronous replication

On 24/09/10 13:57, Simon Riggs wrote:
> If you want high availability you need N+1 redundancy. If you want a
> standby server that is N=1. If you want a highly available standby
> configuration then N+1 = 2.

Yep. Synchronous replication with one standby gives you zero data loss. 
When you add a 2nd standby as you described, then you have a reasonable 
level of high availability as well, as you can continue processing 
transactions in the master even if one slave dies.

> Show me the textbook that describes what happens with 2 standbys. If one
> exists, I'm certain it would agree with my analysis.

I don't disagree with your analysis about multiple standbys and high 
availability. What I'm saying is that in a two standby situation, if 
you're willing to continue operation as usual in the master even if the 
standby is down, you're not doing synchronous replication. Extending 
that to a two standby situation, my claim is that if you're willing to 
continue operation as usual in the master when both standbys are down, 
you're not doing synchronous replication.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com